Method for applying a catalyst to a surface of the catalytic combustion burner

ABSTRACT

The present invention is directed to a method for applying a catalyst to the surface of a catalytic combustion burner that allows better distribution of the catalyst on the surface of the end piece of the burner, and thus prevents too high a temperature at the central zone. The present invention is also directed to a catalytic combustion burner which can be coated with a catalyst in accordance with the method of the invention, and to a catalytic combustion bottle adapted to contain a combustible liquid and to receive at its neck a catalytic combustion burner of the invention.

The present invention pertains generally to the field of catalytic combustion, and more particularly to that of catalytic combustion burners made of porous material. These burners are especially used for diffusing fragrance and/or active substances, for destroying odorous or non-odorous molecules, and/or for purifying air.

A burner of this kind has for example been described in French patent application FR3061543 in the name of the Applicant. This is more particularly a burner intended to receive a wick immersed in a combustible liquid contained in a catalytic combustion bottle, which receives the burner at its neck. A burner of this kind (represented in particular in FIG. 3A) is made of a porous material, which comprises an end piece having on its upper part a cavity emerging to the exterior and on its lower part a cavity in which the end of the wick is engaged. The end piece is extended in its lower part by a sleeve. The outer face of the upper part of the end piece, and its upper face (which is annular), are doped with a catalyst. The same is true, advantageously, of the inner face of the upper part of the end piece. In operation, the combustible liquid conveyed by the wick penetrates into the pores of the porous material of the burner. Part of this liquid crosses the central zone of the burner, where it undergoes vaporization.

It is found, however, that a burner of this kind has the disadvantage, when doped, of leading in operation to an increase in the temperature at the central diffusion zone of the burner, this being detrimental to the olfactory quality when the burner is used for diffusing fragrance.

In order to overcome this aforementioned disadvantage, the Applicant has developed a method for applying the catalyst that allows better distribution of catalyst on the surface of the end piece of the burner, and thus prevents too high a temperature at the central zone.

More particularly, therefore, the present invention is directed to a process for applying a catalyst to the surface of a catalytic combustion burner, said catalytic combustion burner being composed of a porous material and comprising: an end piece with an upper part and a lower part, said upper part having a peripheral side wall comprising an inner face delimiting a cavity, an essentially cylindrical outer face, and a crown-shaped upper face, and a sleeve disposed in the extension of said lower part of said end piece, and comprising a cavity adapted to grip a wick intended to convey a combustible composition to the burner, said method comprising: A) a step of impregnating said outer face and, either, said inner face, said crown of the end piece, or said inner face and said crown, with a catalytic composition comprising at least one catalyst belonging to groups 9 or 10 of the Periodic Table of the Elements; B) a step of heat-treating said burner thus impregnated with the catalyst to a temperature T_(a) of at least 450° C., said method being characterized in that said catalytic composition is a non-newtonian fluid exhibiting, before application on the end piece (1), a dynamic viscosity μ_(c) of at least 15 mPa·s at ambient temperature.

A newtonian fluid is understood in the sense of the present invention to be a fluid whose viscosity is dependent neither on its shear rate nor on the time for which the liquid is sheared.

Advantageously the catalytic composition may comprise: between 1% and 5% by weight, relative to the total weight of the catalytic composition, of a catalyst selected from metals belonging to groups 9 or 10 of the Periodic Table of the Elements, and between 0.2% and 2% by weight, relative to the total weight of the catalytic composition, of a compound capable of increasing the flow resistance of said catalytic composition.

A compound capable of increasing the flow resistance of a fluid is understood in the sense of the present invention to be a compound capable of endowing said fluid with a dynamic viscosity pc of at least 5 mPa·s at ambient temperature (i.e. of the order of 20° C.).

Said compound capable of increasing the flow resistance may preferably be a polymer derived from glucose or a polymer derived from ethylene oxide.

The heat-treatment step B) advantageously comprises the temperature being maintained at T_(a) for at least 3 hours.

The present invention is likewise directed to a catalytic combustion burner which can be coated with a catalyst in accordance with the method of the invention.

Lastly, the present invention is also directed to a catalytic combustion bottle adapted to contain a combustible liquid and to receive at its neck a catalytic combustion burner which receives a wick immersed in said liquid, said bottle (20) being equipped with a burner of the invention.

Other features and advantages of the invention will become clearly apparent from the detailed description thereof which is given hereinafter, for indication and in no way limitation, with reference to the appended figures, in which:

FIG. 1 represents schematically a photograph of an example of a catalytic combustion burner with catalyst, which may have been treated with the method of the invention by impregnation of a catalyst on its surface;

FIG. 2 is a schematic view in elevation of a bottle equipped with the catalytic combustion burner of FIG. 1;

FIG. 3A is an IR thermogram made in order to show the impact of application of the catalyst on the surface of the end piece of a catalytic combustion burner treated by conventional application, in the absence of air conditioning;

FIG. 3Bis an IR thermogram made in order to show the impact of application of the catalyst on the surface of the end piece of a catalytic combustion burner treated by the method of the invention, in the absence of air conditioning;

FIG. 4A is an IR thermogram made in order to show the impact of application of the catalyst on the surface of the end piece of a catalytic combustion burner treated by conventional application, in the presence of air conditioning;

FIG. 4B is an IR thermogram made in order to show the impact of application of the catalyst on the surface of the end piece of a catalytic combustion burner treated by the method of the invention, in the presence of air conditioning;

FIG. 5 illustrates the protocol for measurement by infrared camera of the impact of air conditioning on the temperature of the burner in operation.

The technical features common to [FIG. 1] and [FIG. 2] are each denoted by the same numerical reference in the figures in question.

FIG. 3A, FIG. 3B, FIG. 4A, FIG. 4B and FIG. 5 are discussed in the descriptive part of the examples, which follows the description of FIG. 1 and FIG. 2.

FIG. 1 shows schematically a transverse section through an example of a catalytic combustion burner with catalyst, which can be treated by the method of the invention by impregnation of a catalyst on its surface. A burner 1 of this kind is made of a porous material, which comprises an end piece 1 having on its upper part 10 a cavity (or reservoir) 100 emerging to the exterior, and on its lower part 11 a cavity in which the end of a wick 40 is engaged, this wick 40 being intended to convey to the burner a combustible composition 30 (in the examples below, isopropyl alcohol) from the bottle 20, at whose neck 5 the burner 1 is installed. The end piece 1 is extended in its lower part by a sleeve 2 (also called barrel). FIG. 2 shows schematically in elevation the bottle 20 equipped with the burner 1 of FIG. 1. The combustible liquid 30 is customarily an alcohol, isopropyl alcohol for example, or any other appropriate combustible liquid which is compatible with the legislation in force in this field. The combustible liquid 30 must more particularly be such that its vaporization and its catalytic combustion do not release any unpleasant odour. The combustible liquid 30 may further comprise a fragranced substance and/or an active material.

The wick 40 is any known wick, for example a wick made of cotton, or a wick made of mineral material, for example of mineral fibres. In operation, the combustible liquid 30 from the bottle 20 rises in the wick 40 by capillarity and penetrates into the pores of the porous material of the burner, which, when it has been preheated, carries out catalytic combustion of said liquid. With regard more particularly to the upper part 10 of the end piece 1, the latter has a peripheral side wall comprising an inner, essentially truncated face which delimits a cavity in the form of a reservoir 100, an essentially cylindrical outer face 101, and a crown-shaped upper face 102.

A catalyst (which cannot be seen in FIG. 1 and FIG. 2) has been applied on the outer face 101 and the crown 102 of the end piece 1, either in accordance with the method of the invention (denoted in the examples which follow by “burner BI”), or in accordance with a method which is known to a person skilled in the art (denoted in the examples which follow by “burner BC”). In this latter case, the burner whose doping has been performed conventionally is used as a control in the tests of catalytic operation without and without air conditioning.

For this purpose, to test the catalytic operation (in the presence or absence of air conditioning) of the burner shown in FIG. 1, this burner was disposed in the catalytic combustion bottle 20 shown in FIG. 2.

The burner 10 (either that of the invention as shown in FIG. 5, or that of the prior art as shown in FIG. 1, is installed in the neck 50 of the bottle (by means, for example, of a metallic seat placed in the neck 50). The wick 40 is received inside the burner 10, this catalytic combustion wick 40 receiving a wick (40) immersed in the liquid 30. The bottle 20 may be a bottle of any shape that has a neck 50 into which the burner 10 is fitted.

The examples which follow illustrate the invention, in association with the figures referred to above, but without limiting the scope of the invention.

In these examples, unless otherwise indicated, all percentages and parts are expressed as mass percentages.

EXAMPLES

Devices and compositions

Catalytic composition of the invention

Aqueous, alcoholic or aqueous-alcoholic solvent,

Catalyst:

The catalyst used (whether on parts 100, 101 or 102 of the burner) is a metal belonging to groups 9 or 10 of the Periodic Table of the Elements. It is present at the rate of 2% by weight based on the weight of the catalytic composition of the invention.

Compound capable of increasing the flow resistance of the catalytic composition:

Between 0.2% and 2% by weight, relative to the total weight of the catalytic composition, of a polymer derived from glucose, such that the dynamic viscosity pc of the composition before application is of the order of 20 mPa·s at 20° C.

Control catalytic composition:

Water, Catalyst,

The catalyst used (whether on parts 100, 101 or 102 of the burner) is a metal belonging to groups 9 or 10 of the Periodic Table of the Elements. It is present at the rate of 2% by weight, relative to the weight of the control catalytic composition.

Composition of the porous material of which the burners are composed:

-   thermoconductive compound: silicon carbide (1%), -   refractory compound: mullite (66.5%), -   binder: glass (11.5%), -   pore former: polymethyl methacrylate (PMMA: 21.5%).

Burners used:

Comparative example: doping using the control catalytic composition

Burner “BC” (shown in FIG. 1) composed of a porous material obtained from composition C, with burner faces 100, 101 and 102 being doped with the control catalytic composition, which impregnates them. The catalytic composition is applied on faces 100, 101 and 102 of the end piece of the burner by impregnation and then baking to a temperature of at least 450° C., this temperature being subsequently maintained for at least 3 hours.

Inventive example: doping using the catalytic composition of the invention

Burner “B” (shown in FIG. 1) composed of a porous material obtained from composition C, with burner faces 100, 101 and 102 being doped with the catalytic composition of the invention, which impregnates them. The catalytic composition is applied on faces 100, 101 and 102 of the end piece of the burner by impregnation and then baking to a temperature of at least 450° C., this temperature being subsequently maintained for at least 3 hours.

Bottle used:

That shown in FIG. 2 for the burners “B I” (inventive) and “BC” (comparative or control).

Wick used:

Cotton wicks.

Combustible liquid used:

Isopropyl alcohol.

Tests and measurements

Determination of the operating characteristics of the burners BI and BC installed on the bottle 20, in the presence of an air conditioner at 18° C., with or without ventilation: The test protocol is shown in FIG. 5. It consists overall of using infrared thermography (IR), with the aid of an IR thermal camera, to measure the temperature on each of the burners tested (BI and BC) in operation on the bottle 20, which is placed at a reasonable distance from an air conditioner (the power of which is 800 W in the context of the tests carried out), at the low level of FIG. 4A and FIG. 4B. These measurements, moreover, are compared, for each burner tested (control 1C and inventive 1 and 2), with measurements carried out without ventilation.

The thermograms produced are detailed below:

Control burner BC:

-   Without air conditioning: FIG. 3A, -   With air conditioning: FIG. 4A (top view).

Burner BI treated by the method of the invention:

-   Without air conditioning: FIG. 3B, -   With air conditioning: FIG. 4B (top view).

Comparing the thermograms of FIG. 3A and FIG. 3B, in the absence of air conditioning, shows that the temperature of the diffusion centre zone of the burner decreases from 389° C. (treatment with the control catalytic composition) to 364° C. when the faces 100, 101 and 102 of the end piece of the catalyst are treated by the method of the invention.

A comparison of the thermograms of FIG. 3A and FIG. 3B shows a similar effect in the presence of air conditioning: the temperature of the central diffusion zone zone of the burner decreases from 357° C. (treatment with the control catalytic composition) to 318° C. when the faces 100, 101 and 102 of the end piece of the catalyst are treated by the method of the invention.

Through the application, by the method of the invention, of the catalytic composition having a dynamic viscosity μ_(c) of 15 mPa·s at 20° C., the catalyst penetrates less substantially into the inside of the burner, and so the temperature of the central diffusion zone of the burner is lower than if the control catalytic composition had been applied. 

1. Method for applying a catalyst to the surface of a catalytic combustion burner, said catalytic combustion burner being composed of a porous material and comprising: an end piece with an upper part and a lower part, said upper part having a peripheral side wall comprising an inner face delimiting a cavity, an essentially cylindrical outer face, and a crown-shaped upper face, and a sleeve disposed in the extension of said lower part of said end piece, and comprising a cavity adapted to grip a wick intended to convey a combustible composition to the burner, said method comprising: A) a step of impregnating said outer face and, either, said inner face, said crown of the end piece, or said inner face and said crown, with a catalytic composition comprising at least one catalyst belonging to groups 9 or 10 of the Periodic Table of the Elements; B) a step of heat-treating said burner thus impregnated with the catalyst to a temperature Ta of at least 450° C.; said method being characterized in that said catalytic composition is a non-newtonian fluid exhibiting, before application on the end piece, a dynamic viscosity μ_(c) of at least 15 mPa·s at 20° C.
 2. Method according to claim 1, wherein said catalytic composition comprises: between 1% and 5% by weight, relative to the total weight of the catalytic composition, of a catalyst selected from metals belonging to groups 9 or 10 of the Periodic Table of the Elements, and between 0.2% and 2% by weight, relative to the total weight of the catalytic composition, of a compound capable of increasing the flow resistance of said catalytic composition.
 3. Method according to claim 2, wherein said compound is capable of increasing the flow resistance of a polymer derived from glucose or of a polymer derived from ethylene oxide.
 4. Method according to claim 1, wherein the heat-treatment step B) comprises maintaining the temperature at Ta for at least 3 hours.
 5. Catalytic combustion burner coated with a catalyst applied in accordance with the method as defined in claim
 1. 6. Catalytic combustion bottle, adapted to contain a combustible liquid and to receive at its neck a catalytic combustion burner which receives a wick immersed in said liquid, characterized in that said bottle is equipped with a burner as defined according to claim
 5. 